A wind turbine typically comprises a tower, a nacelle, a hub and a plurality of rotor blades. The rotor blades are attached to the hub. The hub with the rotor blades rotates about a rotor axis of rotation during operation of the wind turbine. In various occasions, a person, e.g. service staff, needs to enter the hub. It may be possible that straight access from the nacelle into the hub is possible. This may, for instance, be possible at gearless, direct drive wind turbines. However, this direct access may be obstructed. In geared wind turbines, typically a gear box impedes direct access from the nacelle into the hub. It should be noted, though, that also in gearless wind turbines direct access may be obstructed for other reasons.
Thus, openings in the hub which allow a person to enter the hub from outside of the hub may be present. Then, the hub is typically equipped with a ladder construction, comprising one ladder for each opening. If, for instance, there are three openings in the hub, three ladders inside the hub exist. If the opening is assumed to be located opposite to the rotor blade, safe and easy access to the hub is only possible if the rotor blade points downward, as only in this position rungs of the ladder are horizontal, and thus only in this position a comfortable and safe access using this ladder is possible. If, however, the rotor blade is in a different position the rungs of the ladder, the ladder being opposite to the rotor blade, are no longer horizontal and it is unsafe for a person entering the hub by the opening.
Thus, there exists an urgent need to provide an access system for a hub of a wind turbine, which allows easier and safer access to the hub compared to conventional access systems.